There is a demand for increasing the recording density of an optical disc. In order to implement an optical disc information device capable of high-density recording and reproduction, it is necessary to increase the recording density in a track direction by reducing the track pitch of an optical disc or to increase the recording density in a linear direction.
As described above, it is effective to reduce the track pitch of an optical disc in order to increase the recording density of an optical disc information device (see e.g. Patent Literature 1).